It is known in the art relating to centrifugal compressors for air and other compressible gases that the operational range of pressure ratios of the compressor may be increased by providing bleed passages in the housing at suitable locations adjacent the impeller. This is particularly useful for engine turbocharger compressors, which are intended to operate over a wide range of rotational speeds under various conditions of engine speed, load and ambient pressure.
In particular cases, air inlet recirculation has been proposed; however, the recirculation passages and the inlet and outlet slots have varied in cross-sectional area and smoothness and have not been designed for flow efficiency.